Device for measuring and analyzing movements of the human body or of parts thereof

ABSTRACT

A device for determining mandibular motion wherein three light emitting diodes at the vertices of a triangle are temporarily fixed to teeth of the subject, the light emitting diodes are sequentially energized, and two sensors responsive to the light emitting diodes are mounted on a headpiece applied to the head of the subject and are trained on the light emitting diodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/FR 89/00593 filed Nov. 17,1989 and based, in turn, upon French national application 88 15484 filedNov. 18, 1988 under the International Convention.

FIELD OF THE INVENTION

The present invention relates to a device for measuring and analyzingthe movements of the human body by electronic means and in particular,the measurement of the mandibular movements with the aim of permittingsimpler and more accurate production of prostheses, rapid diagnosis ofarticular pathologies, and transmission of data which can be useddirectly in a computer-aided design and manufacture technique in thefield of dentistry, such as described in French Patent No. 82/06,707.

BACKGROUND OF THE INVENTION

The various methods prevalent up to 1985 for analyzing mandibularkinematics were based on the use of mechanical instruments all to agreater or lesser extent derived from mandibulographs, whose commercialappearance dated from the 1950s.

Such apparatus permitted the recording of a relatively restrictedexpression of these kinematics, since the expression was limited to theso-called border movements of the mandible. Moreover, the interpretationof the graphs obtained by these methods gave rise to a number of errorsdue to the misunderstanding of the functional cycle and to theintervention of mechanical processes which led to the existence ofartifacts in the graphs.

Another negative aspect of such apparatus is the considerable spacetaken up in the oral cavity in cumbersome and bulky fixation procedureswith which it was impossible to envisage the recording of a normalphysiology of the said kinematics.

The use of apparatuses employing a recording system, which occupieslittle space in the oral cavity and does not in any way interfere withthe masticating cycle, nowadays permits the straightforward recording ofthe functional kinematics which have up till now been remote from oureveryday concerns.

The work carried out by Lundeen and Gibbs had already provided a firstexample of this with the "gnathic replicator". These studies have beenadded to considerably by a large number of authors, who havedemonstrated the more uncertain aspects of the masticating cycles andhave permitted a more exact approach to the phenomena which intervene inthe cycles in term of neuromusculature, quality of the foods crushed,posture of the subject etc.

A number of other apparatuses have attempted to represent as clearly aspossible the data essentially characteristic of the masticatoryapparatus. Mention should be made in particular of the recent workcarried out by Lewin, which has led to the production of the Siemens"sirognathograph", the "Nex K6 diagnostic system" from Myo-tronics Inc,the "LR Candylograph" from Dentron, the "stereognathograph" from Dr.Burchhardt or the Cyberhoby computer pantograph from Denar.

Finally, mention should be made of the "visitrainer" described for thefirst time in 1981 by the team under Professor Hobo and Professor Moriin Japan. It uses an LED (light emitting diode) fixed on the mandibularincisors. At the same period the team under Professor Hobo developed asystem using a charge transfer device (CTD) as a reading means; thewhole assembly is connected to various calculation elements (computer)and their associated peripherals.

These works include the principles developed by Barrie in 1967 and his"photoelectric mandibulography". 1984 saw the appearance of the first"Saphon visitrainer model 1". The latter will soon be followed by the C2model, then the 3 (SVT) model. These models have been developed by thecompany Tokyo Shizaisma C.O. Ltd. and differ in particular in theirergonomic approach (weight, number of points analyzed per second, etc. .. . ).

The fact of having to move a single camera three times in order toanalyze the movements in the horizontal, frontal and sagittal planesprevents these movements from being determined spatially, because asubject never moves his joints in the same manner, and this prevents anyconnection from being made between the three movements.

At the same period Jemt and Karlson showed that the use of two camerasand a diode fixed on the incisors could permit analysis of themandibular movements in three dimensions. In actual fact, this is notcorrect. In particular, it is found that a purely rotational movement,often present in the human body, cannot be detected correctly.

OBJECTS OF THE INVENTION

An object of the present invention is to overcome these disadvantages byproviding analyses in three dimensions, adapted to all odontological andmedical applications, by specifying the means permitting analysis of themovements, and by providing a signal which can be analyzed directly by acomputer, and this in a very rapid manner, while at the same timeaffording the possibility of verification of the analysis, without anyintermediate manual action, as constituted hitherto by the moving of thecameras.

Another object of the invention is to provide an apparatus which iseconomically attractive for the purpose described and is applicable to awide market and which can afford a real saving in time and manpower.

SUMMARY OF THE INVENTION

The device to which the invention relates comprises:

a set of three light emitting diodes fixed in a removable manner on thatpart of the body whose movement is to be analyzed,

two sensors designed to follow the movements of the diodes and mountedon a fixed support in such a way that the diodes are located in theirfield,

and means for controlling the lighting of the diodes, the functioning ofthe sensors and the processing of the data supplied by the latter.

The light emitting diodes advantageously emit in the infrared range andhave an angle of emission of the order of 180°. The light emittingdiodes emit at a wavelength of 900 mm, with a power of approximately 30mW. In the case where the movements of a jaw are being detected, thediodes, which are fixed for example on the incisors, have the advantage,since they emit in the infrared range, of having a certain immunity withregard to the ambient light and of permitting detection when the lipsare closed.

In addition, the angle of emission of 180° permits the simultaneoustracking of the movements by the two sensors. The sensitivity of thesensors is in the region of 900 mm. The overall sampling frequency beingfrom 1 to 2 KHz for a recording period of 20 seconds, the resolutionobtained is substantially greater than that observed with the otherapparatuses described.

This device has synchronization means providing for the successivelighting of the three diodes for brief intervals of time and for thesimultaneous functioning of the sensors.

In addition, this device comprises two signal-shaping stages permittingthe preparation of the data and the transmission thereof fordigitalization, a digitalization stage providing for the analog-digitalconversion of the signal, under the control of the synchronizationmeans, and a storage stage permitting storage of the data and visualdisplay thereof on a graphic monitor. It should be noted that anexternal communication bus permits transmission of all the data to theCAD/CAM system.

The three light emitting diodes are advantageously arranged at the threepoints of a triangle. The positioning of these three diodes makes itpossible to meet the requirements for simultaneous recording of themovement of a point of the mandible relative to three planes which arecurrently used in dentistry, namely the horizontal plane or occlusalplane, the frontal plane and the sagittal plane.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood in any case from the descriptionwhich follows and in which reference is made to the attacheddiagrammatic drawing showing, by way of non-limiting examples, severalembodiments of this device:

FIG. 1 is a perspective view of a first imaging device;

FIG. 2 is a perspective view, on an enlarged scale, of part of thedental arch and of the device for fixing the diodes on the latter;

FIG. 3 is a perspective view of a device for measuring the distancebetween the sensors and the diodes;

FIG. 4 is a highly diagrammatic perspective view showing the use of thedevice in FIG. 3;

FIGS. 5 and 6 are two views corresponding to FIGS. 3 and 4 respectively,showing the device for calculating the distance between the diodes andthe receiver, in a second embodiment;

FIG. 7 is a view of a card for processing the signals;

FIG. 8 is a block diagram of the installation;

FIG. 9 shows the optical trajectory of the measurement;

FIG. 10 is a highly diagrammatic perspective view of the wholeinstallation;

FIG. 11 is a view of a variant of the device for supporting thereceivers;

FIG. 12 is a perspective view of another device for supporting thereceivers;

FIG. 13 is a perspective view of a fork for taking an impression,designed to be used in association with the device in FIG. 12;

FIG. 14 is a partial side view of the fork in FIG. 13;

FIG. 15 is a partial plan view of the fork in FIG. 13;

FIG. 16 is a perspective view of equipment complementing the device inFIG. 12; and

FIG. 17 is a side view of an articulator.

SPECIFIC DESCRIPTION

The various devices shown in the drawing are designed for measuring thedisplacement and analyzing the movements of a jaw. The patient is fittedwith a headpiece 2 provided with means 3 for adjusting its size. On thefront face of the headpiece there are fixed two substantially horizontaland diverging arms 4, at the free end of each of which there is mounteda substantially vertical rod 5 fitted, at its lower end, with aninfrared sensor 6 forming a camera. The position of each sensor 6 can beadjusted both in the direction of the arm 4 and in the direction of thecorresponding rod 5 by means of screws 7, 8, respectively. The arms 4are positioned in such a way that the cameras form between them an angleof between 35° and 120°, and preferably 90°.

In one variant, shown with dot-and-dash lines in FIG. 1, as well as inFIGS. 6 and 10, the two sensors 6 are supported on a single arm 9 andsingle rod 10, which simplifies the adjustments and limits the size.

This device comprises three light emitting diodes 12 which emit in theinfrared range and are fixed on a single support 13 and arranged at thethree points of a triangle. This support 13 is very rigid in order toprevent a relative movement of the diodes 12 during the displacement ofthe organ on which the support is fixed. This support 13 is fixed to arod 14 (FIG. 2) designed to be engaged in a tubular element 15 fixed toa support plate 16 designed to be fixed in a removable manner on theteeth. This fixation is obtained using a photopolymerizable cement. Thediodes are fixed on the teeth in two stages: first the support 15, 16 isfitted on the teeth; then the diode support is forced on this assembly,with stabilization by wedging, by a magnet or else by a spring action.

A sound sensor 17 permits detection of the moment at which the teethcome into contact and separation of each cycle comprising a mastication.

In order to have an exact relationship between the displacements andtheir representation, before carrying out the measurements a graduatedrule is placed between the diodes 12 and the cameras before definitivelyfixing the position of the latter. The position of the cameras isadjusted by acting on the screws 7, 8.

In the embodiment shown in FIG. 3, the device for calibrating thedistance comprises two rods 18 connected to one another by a plate 19designed to bear against the diodes, each rod 18 being fitted at itsother end with a plate 20 designed to bear against the camera. The useof this calibration is shown diagrammatically in FIG. 4. FIGS. 5 and 6show the calibration method in the case where the two sensors 6 aresupported on a single arm. In this case, only one rod 22 is provided,for example mounted slidably on the vertical rod 10 and fitted at itsfree end with a single bearing plate 23.

The data supplied by the cameras are transmitted to an electronic unit24 and processed in an analysis unit 25, with possible connection eitherin the framework of a computer-aided control 26 or a conventionalimaging 27.

The assembly of cameras and diodes is under the control of severalelectronic and data processing stages, which are:

A signal-shaping stage permitting the summation of the succession ofanalysis points in the two planes of the cameras. It is in factimportant to have the overall shape of the curve, and not theorientation of one point.

This stage functions as follows:

reception of the signal,

current/voltage conversion,

voltage input on four differential inputs by diodes,

analog-digital conversion,

input on a computer and, if appropriate, a link to a CAD system.

A calculation stage permitting, by means of appropriate software,transformation of the curves analyzed on the two planes of the camera inprojection to the three planes of the face used in dentistry, namely thehorizontal plane or occlusal plane, the frontal plane and the sagittalplane. The electronic card used is shown in FIG. 7 and comprises amemory 28, a memory/conversion interface 29, a memory/central unitinterface 30, a conversion system 32, and a system 33 forsynchronization of the signals.

Apart from the cards whose functions have already been described,mention should be made of the presence of a memory permitting storage ofthe information arriving in the form of points, in order to constructthe curves, and in particular of the synchronization by means of whichit is possible to light each diode 12 successively and to indicate, foreach sensor 6, which diode is emitting at the moment the light point isreceived.

It is thus possible to receive the respective trajectories of the threepoints on each sensor 6. It is from these six curves that the threecurves specific to the movement are built up and then referred to thethree known dental planes.

FIG. 8 shows the overall system in which the various elements aredesignated by the following references:

The diodes 12 are under the control of the synchronization system 33.This system is also connected to the digitalization stage 34 to whichthe two sensors 6 are connected by way of a formatting stage 35. Thedigitalization stage is connected to the central unit 36, to which thereare connected a visual display screen 37 and a transmission stagedesignated by general reference 38.

As is shown in FIG. 9, the principal axis of emission of a diode 12 hasan angle of emission θ equal to α1+2α2 where α1 is the angle formed bythe orthogonal optical axes 40 of the two sensors 6 and where 2α2 is theangular aperture angle of the optics of the sensors.

The two sensors each define a plane reference line, the two referencelines thus obtained forming with the plane of the diodes a trihedronmaking it possible to locate each emitting diode spatially. If thistrihedron is a straight line trihedron, the subsequent correlationcalculations are eliminated. If one emitting diode defines themovements, except for the centered rotation, two emitters cannot detectthe rotation about the axis of each emitter, while the use of threeemitters permits the detection of all the movements of translation andof rotation.

By way of example, the following values can be used:

duration of recording 20s,

overall sampling frequency 1 KHz,

number of gross samplings 20,000,

number of secondary samplings (3 per gross sampling) 60,000,

four coordinates per secondary sampling 240,000,

number of octets per coordinate: 2,

total number of octets: 480,000.

Between 2,000 and 4,000 values are obtained per cycle of 1 second, whichrepresents an accuracy 10 to 20 times greater than that of knownapparatuses.

In practice, the headpiece 2 is placed on the head of the patient beforefixation of the sensors 6 and calibration by means of the adjustmentdevices 7, 8. The assembly is connected to a computing system includingthe analysis card and comprising in particular an oscilloscope 42, amonitor 37 and, if appropriate, a video recorder 43. The diodes 12 areilluminated alternately and their signal is received by the sensors 6.At the start of the analysis, the jaw of the patient is in a tightocclusion position. The apparatus is started up, after which the patientis asked to carry out a set of movements which it is possible to displayvisually either in an overall fashion or at the level of the variousplanes on which the image is projected by selection using the variousbuttons 44. These data can be simply visually displayed or printed outon paper 45.

Moreover, certain additional information, such as angle calculation,amplitude of movement, time of cycle, can be provided by selection ofbuttons 46.

A direct connection to a CAD/CAM device (computer-aideddesign/computer-aided manufacture) can be used, as described inparticular in French Patent 82/06,707. A dental prosthesis can beconstructed by means of an optical impression, mathematical surfaceproduction of the experimental model as a function of this impression,and direct working. The fact that a wax model is not used makes itnecessary to work on rough surfaces on screen, which prohibits the useof traditional dental articulators.

According to another of its aspects, the present invention makes itpossible to transcribe to the surfaces modeled statically the dynamicmovement when the patient moves his limbs or his jaw. This makes itpossible, on the one hand, to alter certain angles or surfaces whichcould act adversely, but also to develop surface equations integratingthe concept of time.

In order to obtain data on the planes separately or together, withoutknowing the spatial development and ignoring the possible purerotations, the system according to the invention affords the possibilityin its electronic circuit of being able to follow only one diode. Thisanalysis is ensured by a perfectly parallel construction of thecomponents and circuits and by an access to the clock system.

FIG. 11 shows an embodiment for the sensor-supporting device describedabove, in which the same elements are designated by the same referencenumbers. In this case the system, instead of consisting of a headpiece,consists of adjustable spectacles 47 worn by the patient.

FIG. 12 shows yet another device for supporting the sensors. In thisdevice, the headpiece 2 is fitted with two clamps 48 arranged at thelevel of the ears of the patient, and permitting an adjustment, in termsof sliding and in rotation, of the two branches 49 of a cradle 50 whosecentral part, arranged in line with the face of the patient, is fittedwith two clamps 52 each designed for the fitting, with adjustment interms of sliding and in translation, of a rod 53 at the free end ofwhich a sensor 6 is mounted.

The means for locking the clamps 48 and 52 can be purely mechanical orelse pneumatic or hydraulic, which makes it possible to leave theelements completely free until the moment of their locking. In order topermit exploitation of the data obtained on a traditional mechanicalarticulator, the device according to the invention also comprises aspecial fork 54 on which the patient will close his teeth, this forkmaking it possible not only to position the plaster models 55 on anarticulator 56, as shown in FIG. 17, but also to achieve the fixation ofthe diodes on the teeth of the patient.

To this end, the fork 54 comprises, as shown in FIG. 14, a cavity 57 inwhich the device 15, 16 for fixation of the diodes on the teeth isdesigned to be engaged. The plate 58 of the fork is covered on its twosurfaces with a hard impression paste, and the fork is introduced intothe mouth of the patient.

The patient grips the plate between his teeth and marks the impressionof his teeth on the paste, the fixation of the diode support 15, 16being effected at the same time, as well as the adjustment of theposition of the sensors 6. At this point, it is possible to establishthe position of the cameras, the diodes and the tooth impressionsrelative to the axis of rotation of the jaws, which corresponds to theaxis passing through the clamps 48.

In order to modify the occlusal coordinates of a modeled surface, it isnecessary to establish the position of the future prosthesis relative tothe diodes in the case of the application of the device to theproduction of a prosthesis.

To this end, as shown in FIG. 15, the plate 58 of the fork 54 can bemade of a transparent material and comprise an indicator system 59obtained by marking or by engraving.

It is also possible, by virtue of the device according to the invention,to establish the exact height and position of the Frankfort plane, theplane passing through the mouth at the level of the base of the nose andthrough the axis of the ears, relative to the fork 54.

To this end, the device comprises a cradle 60 fixed on the two clamps48, of which the branches are oriented parallel to the facial referenceplane and of which the central part is fitted with a substantiallyvertical rod 62 comprising a member 63 for measuring the position of thefork 54 relative to this plane.

The determination of the position of these points, provided by thedevice according to the invention which is then used as an electronicarticulator, makes it possible to position the plaster impression modelsof the patient on the fork, to set the fork and the impressions in atraditional articulator 56 according to the conventional methods knownat present, and to adjust the values of this articulator (Bennett angle,condylar slope, cusp angle . . . ) taking into account the valuessupplied directly by the device according to the invention. Thistechnique makes it possible to benefit, for the adjustment of thearticulator, from a measurement carried out in a very accurate manner byelectronic means.

As emerges from the above text, the invention brings a considerableimprovement to the existing art by providing a device of simple design,and of very reliable functioning, affording a wide range of possibleuses, while at the same time being very easy for the practitioner touse.

We claim:
 1. A device for measuring and analyzing movements of a part ofa human head of a subject, which comprises:a set of three light emittingdiodes fixed in a removable manner on said part of said head whosemovement is to be analyzed, the three light emitting diodes beingarranged at the three points of a triangle on a common rigid element;two sensors designed to follow the movements of the diodes and mountedon a fixed support in such a way that the diodes are located in fieldsof view of said sensors; means for mounting said support on the head ofthe subject; and means for controlling the lighting of the diodes, thefunctioning of the sensors and the processing of the data supplied bythe latter.
 2. The device as claimed in claim 1, wherein the lightemitting diodes emit in the infrared range and have an angle of emissionof the order of 180°.
 3. The device as claimed in claim 1, which hassynchronization means providing for the successive lighting of the threediodes for brief intervals of time and for the simultaneous functioningof the sensors.
 4. The device as claimed in claim 1, which comprises twosignal-shaping stages permitting preparation of the data andtransmission thereof for digitalization, a digitalization stageproviding for the analog-digital conversion of the signal, under thecontrol of the synchronization means, and a storage stage permittingstorage of the data and visual display thereof on a graphic monitor. 5.The device as claimed in claim 4, wherein, in the case of themeasurement and analysis of the mandibular movements, the means forprocessing the data comprise a stage permitting transformation of thecurves analyzed on the two planes of the sensors in projection onto thethree planes used in dentistry: the horizontal plane or occlusal plane,the frontal plane and the sagittal plane.
 6. The device as claimed inclaim 1, wherein the angle formed by the axes of the two sensors isbetween 35° and 120°.
 7. The device as claimed in claim 6, wherein theangle formed by the axes of the two sensors is 90°.
 8. The device asclaimed in claim 1, wherein the three light emitting diodes are mountedin a definitive manner on a single rigid support designed to be fixed ina removable manner on the body part whose movement is to be analyzed. 9.The device as claimed in claim 8, which, in the case of the measurementand analysis of the mandibular movements, comprises a first supportdesigned to be fixed in a removable manner on a tooth, for example bymeans of a photopolymerizable cement, and to receive the rigid supportbearing the diodes.
 10. The device as claimed in claim 1, which, in thecase of the measurement and analysis of the mandibular movements,comprises a headpiece fitted with at least one arm bearing the twosensors, with the possibility of adjustment of the distance andinclination of the sensors relative to the diodes.
 11. The device asclaimed in claim 10, wherein the headpiece is fitted with two clampswhich, arranged at the level of the ears of the patient, permit anadjustment in terms of sliding and in rotation of the two branches of acradle of which the central part is arranged in line with the face ofthe patient, this central part being fitted with two clamps of axesorthogonal to the first clamps cited, each designed for the fitting,with adjustment in terms of sliding and in rotation, of a rod at thefree end of which is mounted a sensor.
 12. The device as claimed inclaim 11, wherein the two clamps, situated at the level of the ears ofthe patient, are fitted with a cradle of which the branches are orientedparallel to the facial reference plane and of which the central part isfitted with a vertical rod fitted with a member for measuring thedistance between the cradle and the fork.
 13. The device as claimed inclaim 10, wherein the means for adjustment and locking of the rodssupporting the sensor are mechanical.
 14. The device as claimed in claim10, wherein the means for locking the rods supporting the sensor arehydraulic.
 15. The device as claimed in claim 10, which comprises asound sensor permitting determination of the moment at which the teethof the patient come into contact.
 16. The device as claimed in claim 10,which comprises a fork of which one end in plate form is covered, on itstwo surfaces, with hard impression paste, and which is equipped, on oneof its surfaces and set back from the plate, with a cavity bearing thesupport of the diodes, this fork being designed to be introduced intothe mouth of the patient to achieve the fixation of the diodes and thetaking of the impression, while the adjustment of the sensors is carriedout.
 17. The device as claimed in claim 16, wherein the fork is made ofa transparent material and comprises an indicator system.